Harmful sulfurs (elemental and mercaptans) found in many current marketplace gasolines have been shown to induce failure in silver-based fuel gauge sending unit components; these sending unit components are typically mounted in the vehicle's fuel storage tank and are exposed directly to gasoline. Sulfur induces a corrosive film on critical electrical components of the fuel gauge sending unit that disrupts electrical continuity and leads to either erratic operation or complete failure of the sending unit. On many fuel gauge sending unit designs, the erratic operation or failure can give an artificially high level reading on the vehicle's instrument cluster fuel gauge (seen by the driver); this can lead to the vehicle inadvertently running out of fuel, which has serious safety implications under many driving conditions.
Production fuel gauge sending units typically consist of two key electrical components that can be susceptible to sulfur corrosion; a resistive grid element affixed to a ceramic substrate and a contact wiper element that mechanically moves over the resistive grid surface with changes in the fuel level of the storage tank. Because of the design circuit bias, the variable resistance with fuel level changes is seen as a variable voltage which ultimately is shown as movement on the vehicle's fuel gauge as seen by the driver. Increasing resistance of the sending unit is seen as increasing voltage, and decreasing resistance is seen as decreasing voltage. The increased voltage correlates with the increased fuel level in the fuel storage tank which corresponds to the level of the fuel gauge seen by the driver on the instrument panel of the vehicle.
The problem has led to a rash of warranty repair claims at dealerships. Most automotive Original Equipment Manufacturers (OEM) appear to have experienced the problem at some point. The problem typically requires the complete replacement of the fuel gauge sending unit at considerable expense to the OEM or the vehicle owner. Some OEMs have moved towards replacing the silver-based components of the sending units with gold-alloy components. While this is a solution to the problem, it is very expensive and undesireable. Because the silver-based components were first introduced into the marketplace in 1988, over 15 years of manufactured vehicles are still susceptible to the problem.
Metal-filming additives by themselves have been added to bulk gasoline in refineries and in distribution terminals in an attempt to correct abnormally severe batches of gasoline before they reach the marketplace. This is a very expensive procedure and has limited effectiveness because much of the metal filmer additive is lost to the walls of the fuel distribution system before it ever reaches the vehicle's fuel tank. The ideal delivery method for a corrosion inhibitor filming agent is by addition to an aftermarket concentrate package, whereby the package is poured directly into the vehicle's fuel tank and mixed with the gasoline.
Polyether amine fuel additives are well known in the art for the prevention and control of carbonaceous engine deposits. These polyether additives have a poly(oxyalkylene) “backbone”, i.e., the polyether portion of the molecule consists of repeating oxyalkylene units. U.S. Pat. No. 4,191,537, issued Mar. 4, 1980 to Lewis et al., for example, discloses a fuel composition comprising a major portion of hydrocarbons boiling in the gasoline range and from 30 to 2000 ppm of a hydrocarbyl poly(oxyalkylene) aminocarbamate having a molecular weight from about 600 to 10000, and at least one basic nitrogen atom. The hydrocarbyl poly(oxyalkylene) moiety is composed of oxyalkylene units having from 2 to 5 carbon atoms in each oxyalkylene unit. These fuel compositions are taught to maintain the cleanliness of intake systems without contributing to combustion chamber deposits. However, there is nothing in the disclosure to suggest that sulfur-related corrosion problems on silver-based fuel gauge sending units can be rectified at concentrations taught in the disclosure.
U.S. Pat. No. 5,851,242, issued Dec. 22, 1998 to Cherpeck et al., discloses fuel additive compositions containing a polyalkylphenoxyaminoalkane and poly(oxyalkylene) amine that is useful for the prevention and control of engine deposits.
U.S. Pat. No. 5,112,364, issued May 12, 1992 to Rath et al., discloses gasoline-engine fuels which contain from 10 to 2000 parts per million by weight of a polyetheramine and/or a polyetheramine derivative, wherein the polyetheramine is prepared by reductive amination of a phenol-initiated or alkylphenol-initiated polyether alcohol with ammonia or a primary amine
U.S. Pat. No. 5,752,991 issued May 19, 1998 to Plavac, discloses fuel compositions containing from about 50 to about 2500 parts per million by weight of a long chain alkylphenyl poly(oxyalkylene) amine, wherein the alkyl substituent on the phenyl ring has at least 40 carbon atoms.
U.S. Pat. No. 5,853,435 issued Dec. 29, 1998 to Avery et al, discloses a fuel composition containing a multifunctional anti-wear, corrosion inhibiting effective amount of a polymeric amine-heterocyclic additive prepared by the reaction of a hydrocarbyl amine and a sulfur-containing heterocyclic hydrocarbyl compound in a liquid hydrocarbon combustible fuel has excellent high temperature decomposing, cleanliness and detergency/dispersancy features.
While these references primarily deal with prevention and control of carbonaceous engine deposits, they do not address the problem associated with sulfur-related corrosion damage to silver-based fuel gauge sending units.